The wire-electroerosion machining process commonly makes use of an extremely thin tool electrode in the form of a continuous metallic wire of a diameter of 0.02 to 0.3 mm. The wire electrode is vertically passed through a workpiece to define an electroerosion machining gap between them and is axially driven continuously from a supply to a takeup via the machining gap which extends across the thickness of the workpiece. The workpiece is securely mounted in a work receptacle filled with air or open to the atmosphere and typically lies perpendicular to the axis of the traveling wire electrode. A liquid machining medium, e.g. distilled water, is supplied to flood over the region of the wire electrode and the machining gap in the workpiece while a machining electric current is passed between the wire electrode and the workpiece to produce electroerosive material removal from the latter. As material removal proceeds, the receptacle and the wire electrode are relatively displaced, typically perpendicular to the axis of the traveling wire electrode along a prescribed cutting path such that a desired contour is formed in the workpiece. The machining liquid flooding over the cutting region is allowed to fall by gravity on the floor of the work receptacle and then led from the latter to a liquid filtering and circulation system for recycling to the liquid delivery nozzle.
It has generally been accepted that the wire-electroerosion process is highly suitable for machining plastic molds, pressing dies and various other shaped products in due precision and with efficiency. Problems arise, however, when the process is required to form a tapered contour in a workpiece and especially to form the workpiece with a contour having a non-tapered and tapered portions stepped in the direction of the workpiece thickness. Such requirements arise, for example, in a die which should include a straight cutting edge and a tapered relief section. The practice which has been followed heretofore to meet these requirements generally is to use a two-step machining procedure. Thus, in the first step the tapered section is machined with sinking-type electroerosion machine or with a traditional milling and/or grinding machines and in the second step the non-tapered cutting edge section is machined with a wire-electroerosion machine. This procedure is complex, time-consuming and costly. The tapered edge portion has also been machined, in one of the first or second steps, with a modified wire-electroerosion machine which incorporates special facilities to allow the wire electrode to be inclined at an angle with respect to the workpiece surfaces. Although this procedure permits two-step operations with the single equipment, those special facilities entail relatively complex three-axis or four-axis control programming and accordingly adds to further substantial cost and labour. Furthermore, the two-step operation doubles the machining time and is undesirably time-consuming and hence inefficient.